Normally, in order to demount a tire from a rim, the bead breaking of the beads of the tire is first carried out. Then, a first bead of the tire is demounted by forcing it to be gradually brought beyond or outside the edge of the rim adjacent thereto; the rim is then turned until the first bead is completely demounted. At this point, in order to complete the demounting, it is necessary to move the second bead close to the edge of the rim (from which the first bead was demounted), bring the second bead beyond the bead itself, and then proceed in a manner analogous to that carried out for the first bead.
To perform the above, tire mounting-demounting machines have been proposed which are equipped with a rotatable disc designed to push the second bead of the tire from the outside in the direction of the rotation axis of the tire itself, the first bead of such tire having already been demounted. The second bead is pushed until it is brought to abut from the inside against the edge of the rim from which the first bead was demounted. With the rotatable disc, it is not possible to complete the demounting of the second bead by simply rotating the rim, since such disc has its rotation axis substantially parallel to the rotation axis of the rim and thus of the tire, so that during the rotation of the rim, the disc tends to move away from the rim due to the tangential force applied thereto. In order to complete the demounting of the second bead, therefore, an operator must manually intervene. This of course involves considerable physical force for the operator, with the risk of ruining the rim or the tire in case of imprecise or incorrect handling.
Demounting heads or devices have also been proposed that are capable of carrying out all the demounting operations of the second bead of a tire in an automatic manner, hence without requiring the manual intervention of the operator. The European patent EP-1 314 584 teaches a working head comprising a bead breaking roller and a curved tool which can be moved with respect to the roller by means of an actuator along a substantially curved trajectory. More particularly, the tool has a free working end and can be moved between a rest position that is retracted with respect to the roller and a work position in which its free end projects with respect to the roller.
The working head can be used for bead breaking and demounting both the first and the second bead of a tire from a respective rim. With particular reference to the demounting of the second bead, after having bead broken and demounted the first bead, i.e. after having brought it beyond the respective edge of the rim, the head is brought outside the other bead of the tire, and then brought close thereto, in a manner such that the roller is abutted against a portion of the latter bead and pushes it substantially in axial direction up to the level of the first bead of the rim.
At this point, the tool is commanded to come out, in a manner such that its free end is inserted between the free end of the roller and the first edge of the rim in a direction substantially parallel to the rim axis, and it grips a portion of the second bead of the tire. Then, in order to complete the demounting of the second bead of the tire, it is sufficient to rotate the rim.
Such solution, even if it allows demounting the tire from the respective rim in a very efficient manner, is rather complex and costly to obtain.